In the past, it has proved advantageous to apply sealants to ammunition. In order to optimize the sealant material, considerations were given to the sealant's affect on the interior ballistics of the round or the sabot separation mechanism. Specifically, waterproofing materials were sought which would not change the average velocity or the sabot separation mechanism. Optimum was, and is, no net increase in the lubricity of the interfaces between the round and the chamber because it ensures that there is no slipping failure which would keep the round from achieving full velocity. To achieve optimum, typically, relatively weak adhesion/cohesion properties were necessary. However, using sealants with relatively weak adhesion/cohesion properties presented coating problems because the sealant would not readily adhere to the round or sabot if merely dipped into the sealant material. Surface preparation could have been used to increase adhesion properties, but such a procedure, for manufacturing, was, and is, undesirable because it substantially increases the manufacturing operation and reduces manufacturing efficiency.
For coating of ammunition, sealant thickness was also a critical factor in the success of the sealant use. The clearances necessary for chambering of the round were small; the sealant coat had to be uniformly thin. Weapons permitted, for example, no more than 0.0002 in (0.04 mm) clearance in the chamber, so the sealant had to be as thin as possible, adding no more than 0.0001 in (0.02 mm) to the sabot diameter.
Other considerations for optimum sealant effectiveness included minimizing the sealant residue left in the chamber. Foreign material in the chamber increased potential cleaning procedures and increased the risk of foreign material ignition in the chamber.
For sealant application, several methods have been used to apply sealants to small caliber ammunition. These included dipping the round in a pool of sealant material, brushing the sealant material onto the round, and using a spray jet to spray the material onto the surface of the round. None of these methods worked well. For example, in addition to the adhesion problems associated with dipping the flechette cartridge, the round usually had shapes which provided for excess pooling of the sealant at the round nose. Allowing it to air dry also caused bulges or excess of material to form around the sabot nose. Moreover, this pooling or excesses of the sealant created sealant coatings with spot thicknesses in excess of the tolerance specifications.
Brushing the sealant onto the round was an alternative means of applying a sealant coat. However, it was time consuming and impractical. With brush application, quality control was difficult. Coatings applied with paint brushes had excessive thicknesses and uneven sealant layer regardless of attempts at quality control. This technique was only practical on a laboratory scale; brush application was not possible for a manufacturing scale coating operation. A method having limited success was the felt application. A felt application consisted of pressing the sabot into a resilent material in which a hole was drilled. The felt helped to reduce the excess sealant because it cased some of the excess to be wiped off as it was removed from the felt. However, unevenly thick spots in the coating was still a problem.
It was, and still is, desirable for sealant application techniques to be as mechanically simple as possible. Spraying was another prior art method of coating the round. Spray techniques, however, are mechanically complex and have inherent problems with clogging of the spray nozzles with sealant material.
In the manufacturing process, it was also desirable to coat the round with sealant after the round manufacture was complete. It was desirable to apply the sealant to the completed round after all assembly, but before quality assurance. This gave minimum disturbance to existing production lines and provided for a completely coated finished product.
Optimization of manufacturing efficiency with high consistency and repeatability, and uniformity of the thin sealant coat was highly desirable but not achieveable in the past. Because of sabot geometry and sealant viscosity and adhesion/cohesion characteristics, the sealant, then, needed to be physically pressed into the sabot seams and the excess material removed so that the projectile fit into the rifle chamber; none of the prior art procedures provided for application of the necessary consistently thin, uniform sealant coat in a time efficient manner.
Accordingly, there has existed a definite need for a sealant applicator and method of sealant application for ammunition. The present invention satisfies these and other needs, and provides further related advantages.